Conventionally, in mobile communication, ARQ (Automatic Repeat Request) is applied to uplink data transmitted from a radio communication mobile station apparatus (hereinafter simply “mobile station”) to a radio communication base station apparatus (hereinafter simply “base station”) in uplink, and a response signal showing uplink data error detection result is fed back to the mobile station in downlink. CRC (Cyclic Redundancy Check) is performed for the uplink data, and, if CRC=OK (no error), an ACK (Acknowledgment) signal is fed back, and, if CRC=NG (error), a NACK (Negative Acknowledgment) signal is fed back as a response signal to the mobile station.
Recently, to use downlink communication resources efficiently, studies are underway to limit the channels to transmit response signals in downlink to one, and are conducted about ARQ in which this one channel is shared and used by a plurality of mobile stations. Further, in this ARQ, the base station having received uplink data feeds back a response signal to the mobile station after the elapse of a predetermined time period. When a NACK signal is fed back from the base station, the mobile station having received the NACK signal retransmits uplink data to the base station after the elapse of a predetermined time period. Further, in this ARQ, information showing to which mobile station a response signal is addressed does not accompany the response signal (see Non-patent Document 1).
Non-patent Document 1: 3GPP RAN WG1 Meeting document, R1-070245, “Modifications of Uplink Synchronous HARQ scheme,” LG Electronics